If you watched the previous flash flood video:

 This is why when it's raining at all you never go into a gorge or into a dry river bed anywhere in the desert. These folks are obviously tourists and not familiar with what can happen in deserts or they wouldn't have gone into this gorge at all while it was raining anywhere nearby.

But, most people visiting places like this are tourists in cars and 4 wheel drives or smaller motorhomes. So, it's only the locals usually who know not to drive into places like this when it's raining or snowing or hailing anywhere nearby. In the summers when desert monsoons happen in Southern California, Nevada, Arizona, New Mexico, Texas and other places is when it's easy to die if you make this mistake in the western United States.